Alloy steel



Patented May 15, 1945 ALLOY STEEL Luciano G. Selmi, Detroit, andClarence L. Altenburger, Dearborn, Mich., assignors to National SteelCorporation, a corporation of Delaware No Drawing. Application September30, 1942, Serial No. 460,274

4 Claims. (Cl. 75-126) This invention relates to improvements in lowalloy steels. More particularly, the invention relates to steels of thetype disclosed and claimed in applicants Patent No. 2,234,130 issuedMarch 4, 1941.

In the steels described in the foregoing patent, zirconium isincorporated as a constituent to deoxidize the steel and attain aninherently fine grain. In the present invention, by substitutingtitanium for the zirconium in similar steels the many advantages of thesteels of the patent have been retained while eliminating certaindisadvantages inherent in the use of zirconium. These disadvantages inthe use of zirconium in no way affect the characteristics of thepatented steels but appear only during the manufacture. By the presentinvention a similar steel incorporating the same characteristics asthose of the patented steels can be more easily produced, thesubstitution of titanium for the zirconium eliminating many of thepouring and casting troubles encountered With the use of zirconium. Onthe other hand, incorporation of the titanium in place of the zirconiumdoes not deleteriously affeet the physical characteristics of thespecific steel involved. Thus the steel of the present invention hassubstantially the same physical characteristics as the steels disclosedin Patent No. 2,234,130.

Objects of the invention include the provision of an improved hightensile steel; the provision of an improved high tensile steel having amaximum of 0.25% molybdenum and 0.20% titanium; and. the provision of animproved high tensile steel having a maximum of 0.25% carbon.

Other objects of the invention include a provision for a steel whosecomposition shall be variable within definite ranges in accordance withthe size and shape of the finished steel; the provision of an improvedhigh tensile steel capable of being heat treated to predetermined butnarrow ranges of hardness distribution or other physical propertiesdependent thereon.

The above being among the objects of the present invention, the sameconsists in a certain new and useful alloy steel and particularly to oneof new and novel analysis as well as to articles formed therefromwhereby to impart to the same certain desirable characteristics, to behereinafter described and then claimed, having the above and otherobjects in view.

As is well known, many compositions of steel produced with laboratoryfacilities can be balanced chemically so as to produce physicalproperties within a given range. Such compositions may or may not becapable of yielding these same desired properties when subjected to theconditions prevailing in actual commercial steel manufacturing. Rollingtemperatures, rate of cooling after rolling together with the size andshape to the finished material are the main variables aflecting thiscondition.

In the specific case of those steels which have become known to thetrade as low-alloy high tensile steels, in general they are required topossess tensile properties approximately as follows:

Yield point 50,000 psi. min. Tensile strength 70,000 p.s.i. min. Percent elongation in 2 25% min.

Many comparatively simple analyses are capable of producing tensileproperties in the aforesaid range when rolled hot to comparatively thingauges, by controlling finishing temperatures and by the use of copiousapplication of water to the steel on the run out table or cooling bedafter the steel has passed through the last stand of rolls. When thegauge or thickness of strip or plate, for example, increases, suchprocedures become rapidly less effective and tensile properties lowerthan the above minima are obtained from the steel in its rolledcondition.

In the past few years the requirements of low alloy high tensile steelshave increased swiftly. They were originally intended for relativelysimple fabrication methods. Today such steels must weld by allcommercial welding processes as easily as mild carbon steels; they mustbe equal to or better than mild carbon steels in the matter of deepdrawing objects therefrom; they must be capable of responding to theordinary methods of heat treatment and case hardening; they must possessgood notched bar resistance at both normal and sub-normal temperatures,high fatigue resistance, especially fatigue resistance at notches orother stress-raisers which may reside within the body of the steelitself. The steel should have all contained nitrogen fixed in inactiveforms and be free from strain or quench aging. The steel must not be airhardening at any carbon content and should possess no precipitableelements capable of impairing its physical properties upon stressrelieving after Welding or normalizing. This imposing list of propertiesdemanded by modern steel users is due in part to the increasingprecision of modern manufacturing and partly to the increased use oftechnical testing of fabricated structures.

A steel, which Will hereinafter be referred to as steel A, of thefollowing analysis has been found partly to fulfill the above:

Per cent Carbon .05-.25 Manganese .50-.75 Silicon .70-.90 Chromium.45-.75 Titanium .05-.15 Phosphorus .03 max. Sulphur .03 max.

Moreover, hardness distributions across heat treated sections cannot becontrolled to predetermined but narrow ranges except on small or thinshapes.

It has been found in accordance with the present invention that a steel,hereinafter referred to as steel B, of materially better characteristicsthan the above mentioned steel, adapting it to the same and also towider and different fields of use, can be obtained by producing a steelincorporating the same alloying agents as in the steel above mentionedbut containing, in addition thereto, small amounts of molybdenum. Inother words a steel according to the present invention will have thefollowing composition:

Per cent Carbon .05-.25 Manganese .50-1.00 Silicon .50-.90 Chromium.25-.75 Titanium .015-.35 Molybdenum .02-.25 Phosphorus .03 max? Sulphur.03 max,

It is to be understood that although steel A does not equal theperformance of steel B under the conditions set out herein, there aremany conditions under which steel A meets all requirements for a highlydesirable low alloy steel.

Nickel and copper may be present as residual 5 elements. That is, theymay be present in the final steel because of forming an alloying elementof the steel scrap employed in the production of the steel of thepresent invention. Where present as residuals nickel may be present inamounts up to approximately 0.10% and copper in amounts up toapproximately 0.14%. Amounts of nickel up to 0.6% and copper up to 0.3%may occur in the alloy of the present invention without materiallyaffecting the properties thereof, the nickel in the higher amountsperhaps adding some toughness, enhancing the heat treatment andreduction of area to a slight extent, and adding somewhat to thecorrosion resisting properties of the alloy.

In the matter of carburizing, it has been found that the case strengthafter heat treating of both steel A and steel B to compare with thehighest types of alloy steels for carburizing known to the trade. Thecore hardness is too low for 70 many purposes in steel A but steel B,due to its greater hardenability, corrects this condition.

In the specific case of armor plate applications, this is a matter ofparamount importance. In

such applications, one face of the steel plate to be fabricated intoarmor plate is carburized. Thereafter, the plate is heat treated. It isrequired that the face not carburized be not too hard for in that eventa bullet striking the car- 5 burized side may efiect cracking on theother side and throw splinters or particles off therefrom defeating thepurpose of such armor. On the other hand, if the material of the platein regions not carburized be too soft the case will spall off whenstruck by a bullet and hence render that area liable to penetration uponbeing struck by a second bullet thus defeating the purpose of the armor.

When utilizing steel B in heat treated plates, various optimumpercentages of the constituents have been found to exist. The followingtable shows these preferred compositions:

'lliicknws of plate, inches Under it to l 2 and up Per cent carbon 15-.15-. 25 15- 25 Per cent manganese. 50-. 75 .85-. 05 90-1. 00

25 Per cent silicon .50-.00 .50-.00 .50- .90 Per cent chromiuim. 50-. 7560. 70 .60- 70 Per cent molybdenum. 10-. 2O 10-. 20 l0- 20 Per centtitanium 015-. 10 015-. 10 .015- 10 The steel of the present inventionis inherently ne grained and substantially deoxidized.

From the foregoing description it will be seen that the applicants haveproduced a low alloy high tensile steel having its alloy elementsselected, combined and balanced within narrow, but specific and criticalranges, whereby the improved steel having the characteristics andaccomplishing the objects set forth is provided.

Having thus described our invention, the nature and scope thereof aredefined in the ap- 40 pended claims, it being understood that theparticular relationships and ranges specified may be subject to slightor reasonable variation without departing from the spirit of ourinvention.

We claim:

1. A low alloy high tensile steel having deep drawing properties, highfatigue resistance and freedom from strain and quench aging, consistingof carbon .05 to 25%; manganese .50 to 1.00%;

silicon .50 to .90%; chromium .25 to 375%; titanium .015 ,to .20%;molybdenum .02 to 25%; the

balance being iron and incidental impurities.

2. A low alloy high tensile steel having deep drawing properties, highfatigue resistance and freedom from strain and quench aging, consistingof carbon .05 to .25%; manganese .50 to 1.00%; silicon .50 to .90%chromium .25 to .75%; titanium .015 to .l0%; molybdenum .02 to 25%; thebalance bein iron and incidental impurities.

3. A low alloy high tensile steel having deep 60 drawing properties,high fatigue resistance and freedom from strain and quench aging,consisting of carbon .15 to 25%; manganese .50 to 1.00%;

silicon .50 to .90%; chromium .25 to .75%; titanium .015 to .l0%;molybdenum .02 to 25%; the balance being iron and incidental impurities.

4. A low alloy high tensile steel having deep drawing properties, highfatigue resistance and freedom from strain and quench aging, consistingof carbon .15 to 25%; manganese .85 to 1.00%; silicon .50 to .90%;chromium .60 to .70%; titanium .015 to .10%; molybdenum .02 to 25%; thebalance being iron and incidental impurities.

LUCIANO G. SELMI.

